Year	% net
1971	20.92524
1972	20.81935
1973	22.07092
1974	22.54759
1975	23.69834
1976	25.22417
1977	29.18221
1978	31.7409
1979	35.70421
1980	40.40406
1981	48.89858
1982	52.95195
1983	56.37778
1984	58.14528
1985	60.93532
1986	60.64459
1990	49.01772
1992	47.82232
1993	51.04922
1996	58.232
1998	58.89308
1999	67.09651
2000	63.55687
2001	63.35538
2002	61.15713
2003	64.04565
2004	64.76537
2005	62.77374
2006	67.29195
2007	66.68337
2008	64.00752
2010	63.27525
2011	65.36207
2012	67.57606
2013	65.84188
2014	68.70101
2015	71.9013
2016	73.64662
2017	76.0989
2018	76.81635